[ML] Number of executors is set but also dynamic allocation, need to leave only one

As Giacomo originally reported:
In ml_ops.sh there are:
--num-executors ${SPK_EXEC} \
and:
--conf spark.dynamicAllocation.enabled=true \

which trigger the warning:
WARN spark.SparkContext: Dynamic Allocation and num executors both
set, thus dynamic allocation disabled.

Shouldn't we remove the "--num-executors" and add instead:
--conf spark.dynamicAllocation.maxExecutors=${SPK_EXEC} \
?

Still need to determine if we keep it dynamic of fixed number of executors.